When tubulars and/or tubular strings are lowered into or raised out of a wellbore, including, but not limited to, drilling the wellbore, it is common practice, particularly in the oil and gas field, for the tubulars and/or tubular strings to be filled with a fluid or mud. The fluid is typically pumped into the top of the tubular after it has been connected to the tubular string below it and/or as it is being lowered into a wellbore. As the next tubular joint is added to the tubular string, the fluid connection is typically disconnected from the tubular string to allow the next tubular or tubular joint to be connected to the tubular string. When the fluid connection is disconnected, there should preferably to be a valve in place to retain this fluid and prevent it from flowing out onto the work area and environment. The advantages of using such a valve are well known and include saved mud cost, decreased chances of pollution, and increased safety to rig personnel.
In the drilling operation, these valves are typically inserted between the kelly and the tubular string. Typical valves of the mud retaining type are illustrated in the following patents:
PatenteeU.S. Pat. No.Taylor3,331,385Garrett3,698,411Litchfield, et al3,738,436Williamson3,965,980Liljestrand3,967,679
All of the above listed patents include a downwardly opening spring loaded poppet type valve enclosed in a body having at least two parts. These two extra pieces in the drill string replace a conventional single piece kelly saver sub, which functions to reduce wear on the kelly pin. The two-part body is generally longer than a standard kelly saver sub and consequently increases the length of the string which must be handled at the rig. In most oil and gas drilling and/or production operations, it is mandatory that a lower manually operated kelly inside blowout prevention (“IBOP”) safety valve be included in the string at all times, which is another addition to the length of the string which must be handled. Thus, on most oil and gas drilling and/or production rigs, where the height of the derrick or mast is usually limited, it may be impossible to include a mud retaining type valve with a two-part body.
An additional disadvantage inherent in mud retaining valves with two-part bodies is that the pin of the lower body member replaces the pin of the kelly saver sub and is therefore subject to tremendous wear. This wear limits the longevity of the pin and therefore the longevity of the valve. A solution to this problem has been to insert an additional short sub below the lower body member. However, this solution is not entirely satisfactory because it adds still more length to the string.
A further disadvantage of heretofore existing mud retaining valves is in the fact that none of them include means for adjusting the force with which their respective closure members are driven upwardly. The force may be insufficient to close the valve when heavy muds are used.
U.S. Pat. No. 4,128,108 to Bill Parker, et. al. is yet another example of a mud saver valve, and shows in its FIGS. 2 and 3 a mud saver valve which, when the mud pumps are on, mud can flow through the interior of the valve, but which closes when the mud pumps are turned off based upon a spring-loaded closure mechanism which does not have the spring strength to close the valve until the mud pumps are turned off. As with this mud saver valve and with the other ones above referenced, once the mud pumps are turned off, the valve closes and the mud saver valve provides its desired purpose, that of preventing the mud from being spilled out onto the rig floor when the tubular string is being broken down.
The valves disclosed above are unusable in top drive units. In a top drive unit, space below the top drive and above the tubular string is at a premium and must be kept to a minimum. Typically, the conventional top drive comprises two IBOP valve subs. The upper IBOP sub typically contains a remote controlled shut-off valve and the lower IBOP sub typically contains a manual shut-off valve. These valves are typically utilized to prevent damage from wellbore kicks or pressure surges. However, neither of these IBOP sub valves are automatic. Thus, these valves cannot automatically allow fluid or mud flow into the tubulars and/or tubular string, when the mud pumps are running, or prevent flow through the top drive, when the mud pumps are de-energized or shut down. Further, these IBOP sub valves do not provide a simple monitoring of the pressure in the tubular string connected to the top drive. Further, constant use of the IBOP valves as mudsaver valves may cause premature wear requiring costly repair or replacement; in a worst case, the IBOP valves may not be operable when needed to control the wellbore pressure.